means To touch a sensitive part of someone's body lightly so as to cause a twitching, laughing, often squirming sensation — or, figuratively, to gently amuse or please.

from From Old English 'tinclian' or 'ticelian,' to tickle, of uncertain deeper root — possibly imitative, the word itself a little wriggle of sound. It may also be a frequentative or playful reshaping of 'tick,' the light repeated touch. Either way it's an old, homely English word, and the figurative 'tickle your fancy' has been around for centuries, the touch moving inward from skin to mood.